Telephone system



1940. c. w; HALLIGAN 2, 86,

TELEPHONE SYSTEM 7 Filed Oct. 1, 1937 r51. spnows :51

AND

auzzsn TELEPHONE SET BUZZER TO OTHER STATIONS TOLINE AND TO 5 TA TION COMMON CC 7.'

y CM. HALL IGAN 8 WWW A 7' TORNE Y Patented Jan. 9, 1940;

' r. UNITED STATES invention relates to telephone systems and=part1cularly to those which conversational connections between lines orstations are estab- "lished by automatic; means; a

I .The objects of the invention are to minimize. the amount of equipment needed to interconnect stations crimes-selectively in the same system;

to eliminate many of the moving parts hereto-1 foreemployed for such purposes; to simplify the lb 'iunctionsl'performed by the connecting equipment; and to secure other improvements insysterns ofcthi's character.

litrhasbee'mthe practice in thepastto effect conversational connections between the difier entp'arties on a mult'i-party line or between the mdwrduarstations inzintercommunicating sys- :temsbynmeans. of connecting-devices, such as automatic switches, relays, and manually operabl'e keys -And in these prior systems, .where it 39 is desired torsaieguardi the established connections from intrusion by other. stations, this. is

usually accomplished by relay circuitrarrangementsfor excluding other-stations or by some V form of, electromechanical lockout device.

" 25 According to-thepresent invention advantages are rse'cured over these prior arrangements by eliminating the connection establishing switches andi'relays and byreplacingthemnrith. simple resistor elements 'havingtthe necessaryresistance 39 characteristics toflisolate" effectively eachstation from all other stations in the's'ystem and also to render any ltwoustationaunder the control of one of .theni,' effective for conversation to the exclusioriof all remaining stations. To this end 35 the talking". conductors of each station in the system are provided with variable resistance ,ele-

mentsgsuch as those having high negative temperaturefcoeflicient's' of. resistance. The normal 7 resistance of these elements is sufficiently high 49 to prevent the flow of current from a common source over the talking conductors of the ico'rre-j spending? stations, although the common sourcemay be connected in. a permanent and continu- I ou's'circuit to each of the stations. Whemhow- 45 ever the' temperature of the resistance element's associated with any particular station is increased-"either by ithe application of external heat or by increasing the'poten'tial applied to the I elements, their resistance is substantially den creased to'permitrthe'flow of talking 'current'to such station The party at any one of-the stations may establish a talking conditionbetween his station and the station'of a particularv party withwh'om he'wants to converse, to the exclusioxi off alliother' stations",by .m.eans under. his

control, such askeys, whereby he may bring abouta decrease inthe resistance of the elements pertaining to hisstation and those pertaining to the called station, disablingat the same time the control of ,all remaining sta'tionsover the resist- I! ance-elements, associated with said remaining stations; I

A feature of the invention -a multi station system in which: there is a mutually exclusive relationship betweeneach's-tation and one or more 10 oi? the other stations, and inwhich certain stations are alwayssubordinate toone of the other stations. .According ftoathis-ieature the several stations are permanently connected to "the common line by means of talking branch circuits, 1 5

' each of which includes variable resistance ele merits in the talking conductors; I These elements are soarranged that any one of the stations initiating a call causes its.,resistanceelements to lower their resistance and renderthe station efm fective for conversation. Certain stations when thus seizing the line for theirvown individual use alter the. potential of the line such that other stations attempting to call later are prevented iromdoing so because such subsequent calling stations do notv receive suiiicient current'through theirnresistance elements to alter the resistance of these elements." Certain other stations, howevenTalthough mutually exclusive among them- I I selves, are always subordinate to particular sta- I 4 ti onson the line.v In other words; these subordinate stations may appropriate the line for use prov'ided it is idle, but any one 'oiithe preferredstations may seize the, line at any time,

thereby excludingthe subordinate station al- I though it. is using the line at the time.

, The foregoing 'andother features of the in vention will be described more ruuy' inthe following specification. I l v if;

'In the drawing whichaccompanies the speci- 4 Fig.; 1 illustrates an intercommunicating systemyincluding' a'number of stations and acomv men line circuit; A,

vidual stations shown Fig. 1; and

n Fig. '3 illustrates a .multi-party line Land. an

operators cord "circuit atj-theicentral' office for making .connections'with said line.

"In the systems illustrating the present inven tion the intercommunlcating'station lines and the'f'multi-"party' stations are 'joined directly to the common line, over which talking current is supplied to'the telephone instruments at the respective sta'tions Toren'der the stations norw 2 shows a modified circuit for the indie 0 the remaining stations.

tion in the resistance values either by applying s external heat to them or by raising the potential applied to the circuits in which these elements are used. The effects of this large reduction in resistance of the elements many-selected station line circuit is to change the line virtually from an open to a closed circuitcondition. Moreover, the characteristics of these -materials are such that the resistance elements may be so designedv and arranged in the system that the large reduction in the resistance of the elements individual to a particular station lowers to such an extent the potential available for other stations that such other stations are disabled and are prevented from similarly lowering the resistance of their elements to render them effective for conversation. I v

A detailed description will now be given of the systems illustrated in the. drawing.

The intercommunica'ting system shown in Fig. 1 comprises a plurality of individual stations, including stations S-I, S --2 and S-'--3. Each station is equipped with any suitable telephone set and also with some form of signaling device, such as a buzzer I. The several station lines; .or branches 2,3,1, etc., each of which comprises two continuous talking conductors, are connected directly to the corresponding conductors of the common current-supply circuit 5. Talking battery is supplied to the common circuit 5 through the windings of a choke coil 6.

Each of the talking conductors of each station line includes therein a variable-resistance :element, and it willbe noted that these resistors are the only elements in the talking conductors between theindividual station and the common supply circuit 5. The elements I and 8 in the station line 2 are designed to alter their re-' sistance when heated by either one of the heating windings 9 and I0. Both of these windings are arranged in close proximity to the resistors I and 8, and the heat produced by the energization of either winding alone issuflicient to lower the resistance of both elements I and 8 to the point where talking current flows freely from the common circuit 5 to the conductors of the station line 2. Similarly the station line 3 is equipped with variable-resistance elements II and I2 and with heating coi1sjI3 and I4,andthe station line 4 is equipped with variable-resistance elements I5 and I6 and with heat coils I1 and I 8. And other stations in the system are similarly equipped. a

The several stations are provided with selecting keys, each station having as many keys as there arev other stations inthe system. Station S--l for example is provided with a key I9 for callin station S-2, with a key 29 for calling station S-3 and similarly with other keys for The keys I9, 20, etc., at station S.I are normally. connected in series circuit including resistance element 2| and the heating coil 9... The element 2| is designed to 1 ofier a normal, high resistance to the flow of cur:

rent therein and to lower its resistance when 8.

sufficient voltage is applied thereto to cause heating current to flow through the element. In a similar manner station S-2 is equipped with keys 22, 23 for calling stations S--I and S3, respectively, and with the resistance element 24; and station S-3 is equipped withkeys 25, 26 for calling stations S-I and S2 and with the re- I sistance element .21.

Each'of the heating coils Ill, I;, I 8 ,.,etc., has

one of its terminals connected through a common resistance 28 to battery. The other terminal of coil I9 is connected to contacts of keys 22, 25, etc., at the remaining stations. Similarly, the other terminals of coils I4 and I8, individual to the stationlines 3 and 4, are connected to the 'mally connects the buzzer'I across the talking conductors and closing the two talking conductors in a loop including the telephone transmitter. .A continuous circuit now exists from battery through the right Winding of coil 6 over conductor 29 through the resistor 8, over talking conductor 30,through the switchhook contacts and transmitter, thence over talking conductor 3|, resistor I, and conductor 32,'throughthe left winding of coil 6 to ground. The resistance of elements 'I and 8 is .so high, however, that no appreciable current fiowsto the station S-I. Next, the calling party operates'the key 29 to select the. called station 5-3. The closure 'of'key 2B completesa circuit from ground through the heating coil 9 associated with the calling station line 2, resistance element 2|, normal contacts of key I9, operated contact of key 29, conductor 33, through the heating "coil I8 associated with the called station line 4, thence through the common resistance 28 to. battery. The closure of this circuit applies a potential acrossthe terminals of the resistance element 2I. This I potential causes a comparatively small current to flow through the element 2|, gradually raising its temperature and lowering its resistance, permit ting the currentfflow to increase until full heat ing current is flowing through the coils 9 and I8. The heat produced by coil 9 lowers the resistance of elements I and 8, permitting the full flow of current from the supply circuit 5 over, the sta-' tion line 2 to energize the transmitterat the station S-I. Likewise, the heat produced by coil I8 lowers the resistanceelements I51and I6 to permit the flow of current from the supply circuit 5 overthe conductors 34 and 35 and through the buzzer at the called station 5-3. The buzzer operates and attractsthe attention of the party at station S3. When the called party answers byremoving his receiver from the switchhook, his buzzer is disconnected, and his transmitter is connected in a loop circuit and'receives full energizing current from the common supply circuit 5. The parties at, stations S-I and S-3 may now converse with each other. v 1 j Should one of the other parties, such'as' the partyat station.S- 2, attempt to call the busy station S--I, he will be prevented from doing so by reason of the fact that there is insuffici'ent a tential available for lowering the resistance of the element 24.' When the party at station 8+2 closes the key 22 in his attempt to seize the Stavpotentisiibeins iappliedtenths-elements 42 and 4.3,-=thyximmediately"lower their'resistance and avenues is closedr-irom-esround through heating? coil i 3," resistor 24-, operatectcontacts' (if-key 22,'c0nductor 36, heating'coil lfl "through common resistance 28 to battery. Howeverrthe flow of current through the common re-- sistance 28 by way of heating coils I8.-and -9 reduces the potential of 'theHlef-t-handrtermi'nal ofresistance 28 to the point where it is: insufficient to cause the flow of energizingcurrent through the resistancetelement 24 andcoil I3 when the key 22 is closed; Consequently ---the closure of key 22 at-the-station S-J isinefi'ective to-lower theresistance'of theelements' I I and I2, and'the station ,S-2 remains excludedfrom the connection; In like manner, all otherstations are disabled from establishing-conversational connections either between themselves or with either of the engaged stations S-I "and At the end of the conversationbetween-the parties at statiohs'S-I and S-33they replace their receivers on the switchhook and the calling party at station SI releases the selected key l9 to'its normal position. Thereupon the re sistance of elements I, 8, I5, I6 and 2| restore.

to their normal high-resistance values, and the systemis returned to the common use of all of the stations. I

Fig. 2 illustrates a modified station line circuit in which the resistance-elements It and 8- v and'the heating coils 9 and I0 of-Fig-lare replaced by a relay 3'! having two windings? The winding 38 replaces the heatingcoil I0 andserves when energized by the depression of a key at some. other station to operate'the relay and close r 48 and 49, which are connected as shown. The

line 4| terminates at the central oifice in a jack 5!], and through the normal contacts of this jack'the line conductors are connected to a signal lamp 5i and a source or current. The jack 50 appears at an operator's position, which is equipped with cord circuits, such as the cord C, for establishing connections between the line 4| and other lines in the exchange.

The resistance elements 43 to 49, inclusive, are designed to ofier high resistance to theflow of current when the potentials applied thereto are below certain critical or required values. How

ever, when sufiicient potential is applied to these resistorstheyrapidly lower their resistance and permit full current flow in the conductors to whichthey are connected.

Assuming that all stations on line are in their normal condition, any one of these stations may seize the line'by the mere act on the part of the party at the station of removing the receiver from the switchhook. Assume first that the party at station S4 removes his receiver to! make a call. The removal of the receiver closes a circuit from battery to the lamp 5|, thence over conductor 53 through element 42 through the substation loop, element 43, conductor 54 through the contact of jack 50 to ground. Full .allowjfifull energizing current to flow through the loop of the. substation. 'Also the ,lamp 5 I lights,

and the operatorrirepli'es"to thecall in 'the usual mannerF-iWhileJ the line is thus in a calling condition; any one .ofthe other stations S5, 3-16 and,S'I is; excluded from the line by reason of theiactthat'asubstantial-part of the ,potential drop ls=consumed by the flow of ourrent through the lamp 5i, resistors 42 and 43 of thes'l'iation S- 4; andthat-rem'aining is insufficientjtoflowerthe resistance of any of the other resistance elements; i'I'herefore, the resistance elements of stations S-5, S--6 and S-I remain suiiicientl-y highj even-though the receiver at any one" of -thesestationsymay be removed, to pre- I ventenough' current flow to enable any one of these-parties either to'listen or. to interfere with the-stationS-J. f I r eln aw similarmanner.-the station S'5 may initiate -'a cal-l' and exclude all of the remaining 1 threestations S--4, S- B and" S 'I. Likewise,

stations S-B and-S-'I;are mutually exclusive.

When station S6 initiates a call, current flows over the conductor 53 through the resistance element 42, through there'sistance element 46, loop ofstation "8 -6;- resistance'elements 41 and 43 and thence to ground. The' full potential of the battery is 'sufilcient to lower the resistance of all four' 'elements 42, '43, 45 and -41, enabling the station's-:6 to seize the linefor conversation.

And the same is true'when' the stations-*1 ini-, "tiatesna call'.- However, shouldthe-party at station S-'+4="remove his receiver while either station -S5 or -S -"I is in a conditionffor conversation,: th'e shunt atth'e station S4 lowers the potential acrossthe branchextending to the sta .tion S-+6 and 'S-'-I'. Therefore, the calling sta tion S6 or 8-1 is automatically excluded and disabled from further conversation by the pre- "ferred'station S"4. Thestation'S'5, being connected in parallel relation with stations S6 and S--I cannot take control of a connection already established by either of the stations S-"-6'-andS"I.' a *1 What is claimed is:

1. The combination in a telephone telephone station, a source for supplying talking current to said station, two talking conductors permanently joining said source to said station,

elements in said talking conductors having a system of a' I normal resistance sufiiciently high to prevent the flow of talking current to said station, and means eflective upon the initiation of. a call at said station for lowering the resistance of said ele ments to permit talking current to flow to said v i station.

2. The combination in a telephone system of a plurality of stations, each equipped with av telephone, a source of current common tosaid stations for supplying energy to said telephones,

each station provided with a continuous and permanent talking circuit extending therefrom to said common source of'current, means under the sole control of the party at each station for opening and closing the talking circuit of said cuits for controlling the amount of current flowing from said source to the respective stations.

3. The combination in a telephone system of e a plurality of stations, each equipped with a tele.-' phone, a source of current common to said sta-,

tions for supplying energy to said telephones,

each station provided with an unbroken talking source.

path extending ther'etromto said common source of current, variable-resistance elements in said talking circuits having normal resistance values sufiic'iently high to prevent the flow of current from said source to the respective stations, and selective means'for lowering the resistance of the elements in the talking circuit of a' particular station to enable current to flow from the resistance of the elements in the talking'circuit of ,such station to enable the flow of current in said talking *circuitfrom said common 5., In a telephone system, a plurality of stations, a'source common to said stations for supplying talking current thereto, each station equipped with a talking circuit comprising two conductors extending therefrom to said source of current, variable-resistance elements included respectively in the talking circuits of said stations and serving normally to, prevent the flow of current from said source to said stations, and selective means controlled by the party at any one of said stations for altering the resistance of the elements associated withhis station and with any one of the stations he desires to call to enable the flow of energizing current from said source both to his station and to the called station.

6. In a telephone system, a line, a plurality of stations, talking branches one for each station permanently connected to said line and extending in a continuous path to the respective sta-, tions, variable-resistance elements in said branches, a common source of talking current, and means for applying said source to the line to vary the resistance of said elements'and allow current to flow to any station that is in a calling condition to the exclusion of other stations that are not in a calling condition and to allow current to flow to a particular calling station to the exclusion of a particular other station that is already in a calling condition.

. 7. In ,a telephone system, a line, a plurality of stations, each having unbroken talking conductors permanently connected between the station andsaid line, variable-resistance elements, one for each of said talking circuits, a common source of talking-current,. means for applying said source to lower the resistance of the element associated with any calling station to theexclusion of another of said calling stations if the latter is in a non-calling condition and for applying said source to lower the resistance of the element associated with a particular calling line station to the exclusion of a particular other station whether or not the latter is in a calling condition.

8. In a telephone system, a line, a plurality of stations, each having a talking branch permanently connected to said line and extending without interruption to the corresponding station, thermo-sensitive resistance elements in each of said branches having, normal resistances sufficiently high to prevent the flow of current over the line to the corresponding station, a source of current common to said stations for heating the elements in any one of said branches, circuit means under the control of a calling one of said stations for causing heating current to flow from said source to selectively heat the resistance elements in the corresponding branch, said elements automatically lowering their resistances to permit the flow of energizing current from said source over the line to the calling station, and means common to said stations effective to reduce the heating current available from said source to a value insufficient to lower the resistance of the elements associated with a second station in the event said second station subsequently attempts to seize saidline.

CLAIR W. HALLIGAN. 

